The invention relates to a dehumidifier unit for dehumidifying air in a container having at least one Peltier element. Furthermore the invention relates to a container, in particular to a power converter container, having a dehumidifier unit of this type and also to a vehicle, in particular to a rail vehicle, having a dehumidifier unit of this type. Furthermore the invention relates to a method for dehumidifying air in the interior of a container.
Dehumidification serves to protect electronic or power electronics components and modules. These are mostly arranged in containers. In vehicles such as rail vehicles for example these containers are often embodied as underfloor containers, roof containers and locomotive power converter containers complying with protection type IP54, in order to offer a defined minimum level of protection from environmental influences for the technical components enclosed in said container and for the overall system. However the intrusion of humidity into the container is not prevented or is only inadequately prevented by this type of protection.
Possible effects of humidity are occurrences of corrosion and migration at semiconductor structures and solder, in particular at non-encapsulated power semiconductors, with significant potential for damage and the effect of reducing the service life even far below the permitted values for relative air humidity given in the data sheets.
A completely airtight embodiment of containers for protection of electronic components is expensive and associated with a high weight of the corresponding container. However it is precisely for vehicles that the market demands low-cost and lightweight solutions.
A further possibility for reducing the air humidity in the interior of containers consists of introducing into these containers drying agents, such as gel drying agents that extract humidity from the air for example. The disadvantage that exists here however is that these drying agents have to be replaced at regular intervals when the gel becomes saturated. This gives rise to short maintenance intervals precisely in regions of high air humidity or where air humidity fluctuates greatly. This maintenance work restricts the availability of the corresponding device or vehicle and above and beyond this increases the costs for operation. The external regeneration of the drying agent or the use of new drying agent further increases the costs when using these drying agents.
Commercially-available switching cabinet cooling devices with a coolant circuit, which in some cases, when expanded by means of additional parts, are suitable for dehumidifying air, are driven as a rule by an alternating current motor. These have the disadvantage of a relatively complex construction with a comparatively high space requirement.
Furthermore Peltier-effect dehumidifier units are available on the market for use in switching cabinets, inter alia with wall mounting, for an ambient temperature of up to around 30° C. In such devices the warm side of the dehumidifier unit is attached to the wall such that the warm side will be cooled by the air outside the switching cabinet and humidity condenses on the cold side, embodied as a condensation plate for example, in the interior of the switching cabinet. Stationary systems and installations in the outdoor area, e.g. for telecommunications, are equipped with this planned and prepared wall mounting, in order to make use of the potentially lower outside temperature, which is of advantage for the function of the device and for a low use of energy.
The stronger is the undercooling of the cold side (between approximately 0° C. and dew point temperature >0° C.) the greater is the condensation power and also the also the minimal air humidity that can be achieved at a specific air temperature. Condensation power refers to the quantity of condensed humidity per unit of time.
To increase the cooling power a number of Peltier elements will usually be arranged in parallel.
In a few application cases, such as for example for use in vehicles, it has turned out to be disadvantageous to provide a cutout in the outer walls of switching cabinets or other containers, into which a dehumidification unit can be introduced, in order to cool its warm side with the ambient air. Then, by comparison with such containers with a closed surface, these containers have a greatly reduced stability. In order to achieve the desired or required mechanical stability the container must be strengthened for example by the introduction of further struts. This in its turn is at the expense of the weight of the container and thus of a vehicle equipped therewith.